In packet switched transmissions, data transmitted between two equipments are organized into packets which include the information on the recipient of the packet. Packets sent from a user equipment, are received by the network that routes them to the final recipient, e.g. another user or a network server.
Since a public network provides services to a huge number of users sharing the same physical resources, resource allocation is of paramount importance to serve all users with the necessary Quality of Service (QoS).
An efficient resource allocation should take into account several parameters like Quality of Service (QoS) requirements, channel conditions of different users, priorities between different classes of services.
Packet scheduling is therefore an important task of the network, which is furthermore complicated in OFDMA (Orthogonal Frequency Division Multiplexing Access) networks (like Long Term Evolution—LTE), wherein resources shall be managed both in time and in frequency.
In LTE, the elementary radio resource for the scheduler is the TTI (Time Transmission Interval) which is divided in two parts (along the time dimension): control region (carrying control channels, e.g. PDCCH—Physical Downlink Control Channel) and data region (carrying data channels, e.g. PDSCH—Physical Downlink Shared Channel). These two regions are adjacent in the time dimension, and the total occupation is equal to 14 OFDMA symbols (in case of normal cyclic prefix).
The length of the control region can be set to 2-3-4 OFDMA symbols (in case of TTI containing up to 10 Physical Resource Blocks (PRBs)) or 1-2-3 OFDMA symbols (in case of TTI containing more than 10 PRBs), and this switching point between control and data region can be set by the system with a certain degree of freedom.
Known network solutions provides for fixing the number of OFDM symbols intended for DCI before deciding how to allocate data packets in the remaining data region. In other words, the known solutions provide first for deciding how many network resources are to be dedicated to downlink control information (DCI) and than for allocating the data packets in the remaining resources of the TTI.
UK patent application GB 2434279A discloses a method for resource allocation in a communication system. The method comprises setting specific time and frequency chunks within a band to provide localised resources for localised and distributed users. The signalling resources allocation for each user is in the chunk at the same frequency range of the allocated resources, or a subset of the frequency range. Scientific article “HARQ Aware Frequency Domain Packet Scheduler with different degrees of fairness for the UTRAN Long Term Evolution” (published in Proceedings of the IEEE Vehicular Technology Conference (VTC), Dublin, Ireland, April 2007, by Pokhariyal, K. I. Pedersen, G. Monghal, I. Z. Kovacs, C. Rosa, T. E. Kolding, and P. E. Mogensen), discloses that by dividing the packet scheduler into a time domain and a frequency domain part the fairness between users can be effectively controlled. Different algorithms are applied in each scheduling part.
In the literature several other scheduling algorithms for OFDMA systems are known. In particular, scientific articles ‘Optimal Power Allocation in Multiuser OFDM Systems’, (published in IEEE GLOBECOM 2003 by Z. Shen, J. Andrews, B. Evans), ‘Fair OFDMA Scheduling Algorithm Using Iterative Local Search with k-opt-Switches’, (2008 by A. Ibing, H. Boche) and “MAC Scheduling Scheme for VoIP Traffic Service in 3G LTE”, (published in VTC'2007, pp. 1441-1445, by S. Choi, K. Jun, Y. Shin, S. Kang, B. Choi) propose scheduling algorithms for OFDM systems. These articles do not consider separation between control region and data region in the radio subframe; the final solution is related only to a data region of OFDM subcarriers.
Applicants have perceived that, although several packet scheduling algorithms are known in the art, known solutions are not always that efficient, since they do not consider a cross dependency between data region and control region in terms of capacity. Since user data is transmitted over PDSCH (Physical Downlink Shared Channel) and scheduled in the TTI in a certain number of data packets (Transport Blocks), the system capacity depends on the number and on the size of Transport Blocks (TBs) scheduled in each TTI. Moreover, since the propagation environment is characterized by a fast fading process, the frequency selectivity of the channel quality is an important issue to be taken into account during the resource allocation phase (i.e. the choice of the frequency position in terms of PRBs occupied within a TTI of a certain TB to be transmitted); in fact, the spectral efficiency of a TB transmitted in a TTI depends also on the set of used PRBs in that TTI, then also the overall capacity depends on the particular resource allocation algorithm used.
Finally, since the switching point between control region and data region determines the amount of resources destined to these regions, the system capacity depends also on this parameter: as a consequence the number of OFDMA symbols reserved to the control influences the capacity of the data region; on the other side also the amount of resources reserved to the data region influences the capacity in the control region, with a consequent cross-dependence of the two regions in the TTI.
As a result, in general the optimal choice of the switching point depends on users channel conditions but also on the set of packets to be scheduled, and on the other side the number of packets that it's possible to transmit depends in turn on the switching point.
There's therefore the need for a packet scheduling method which takes into consideration also this cross dependency between control and data region of a TTI, so as to improve scheduling efficiency.